Fume hood



H. s. MORROW FUME HOOD Feb. 3, 1953 5 Sheets-Sheet 1 Filed Nov. 4, 1950Feb. 3, 1953 MQRRQW 2,627,220

FUME HOOD Filed Nov. 4, 1950 3 Sheets-Sheet 2 ORROW Feb. 3, 1953 FUMEnoon 5 Sheets-sh 5 Filed 4, 1950 aga Patented Feb. 3, 1953 FUME HOODHarry S. Morrow, Muskegon, Mich., assignor to E. H. Sheldon & 00.,Muskegon, Mich, a cor- V poration of Michigan Application November 4,1950, Serial No. 194,176

8 Claims.

My invention relates generally to fume hoods forming parts of laboratoryequipment for exhausting to the atmosphere toxic and noxious fumes whichmay be formed as a result of various chemical reactions which take placewithin the hood. More particularly, my invention relates to pressurizedhoods for air conditioned laboratories, in which the amount of air drawninto the hood from the laboratory room is greatly reduced as comparedwith conventional fume exhausting hoods used in chemical and otherlaboratories.

In conventional fume hoods, the gaseous fumes resulting from chemicalreactions are drawn by a suction fan through the opening in the hood andexhausted to the atmosphere. In order that all of the fumes be drawninto the suction conduit and none escape to the room through the workingopening in the hood, a relatively large capacity suction fan must beemployed, and this results in the withdrawal of a large amount of airfrom the l room in which the hood is located. In most laboratories theair in the room must be heated or cooled during at least portions of theyear, and may have to have its humidity reduced by suitable airconditioning apparatus. The withdrawal of the large quantity of air fromthe room to prevent escape of the fumes into the room, and to provideadequate dilution of the fumes in such prior systerns, makes itnecessary that the capacity of the heating or air conditionin equipment,or both, be very large and correspondingly costly. This is because alarge working opening in the hood is required, this opening beingusually in the order of two to three feet in height, and four to fivefeet in width, and because a lineal air speed of 70 feet per minute isdesirable to provide adequate dilution of the fumes and to preventescape of the fumes into the room.

Assuming, for example, that the hood has an opening of ten square feet,700 cubic feet of air per minute would be drawn from the laboratorythrough a single fume hood. The laboratory may have a number of suchhoods, and the volume of conditioned air removed from the laboratoryroom would be correspondingly multiplied. Such loss of conditioned airfrom the laboratory room is greatly reduced by the use of the fume hoodof my invention, and is accomplished in part by supplying atmosphericair under positive pressure to the fume hood, as Well as by creating anegative pressure area for the exhaust of the polluted air to theatmosphere. Further, the fume hood is so constructed that theatmospheric air under positive pressure forced into the hood, due to aVenturi-like effect, causes a slight negative pressure zone within thehood, to which. air may flow at a relatively slow linear speed throughthe working opening in the fume hood and thus be admixed with the freshair and fumes and exhausted from the hood through a plenum chamberconnected to an exhaust conduit in which the negative pressure ismaintained.

For most installations I have discovered that of the total air removedfrom the hood it is practical to exhaust as little as twenty per centthrough the Working opening of the hood, the remaining eighty per centbeing atmospheric air forced into the hood by a blower drawing airdirectly from the atmosphere. As a result, the load on the heating orair conditioning equipment, due to the use of the fume hood, or hoods,is reduced to approximately one-fifth of that which it would be if allof the air used for withdrawing and diluting the fumes generated withinthe hood were taken from the laboratoryroom.

Furthermore, since the lineal speed of the air passing through the hoodopening is greatly reduced, there is less turbulence which wouldinterfere with the gas flames of Busen burners or the like, and there isconsequently less cooling of heating apparatus and accessories which-areused within the hood. In addition, because the lineal speed of the airflowing through the working opening of the fume hood isgreatly reduced,the

formerly objectionable draft upon the person working at the fume hoodopening is substantially eliminated.

All of these factors added together, render the fume hood of myinvention much more efficient than those af the prior art, with respectloothto the total amount of equipment necessary for the heating or airconditioning apparatus, oryboth, and for the exhaust of the fumes fromthe hood, as well as reducing the amount of power required for theoperation of such equipment.

It is therefore the primary object of my invention to provide animproved fume exhaust hood ,in which only aportion of the air used tocarry away fumes from the hood is supplied from the room in which thehood is located.

A further-object is to provide an improved fume hood in which isincludedimproved bafiling means Fig. 2 is a vertical sectional view taken on theline 22 of Fig. l, and to an enlarged scale;

Fig. 3 is an enlarged scale fragmentary horizontal sectional view takenon the line 33 of Fig. 1;

Fig. 4 is a vertical sectional view taken on the line 4-4 of Fig. 2;

Fig. 5 is a front 'elevational view of a modified form of hood, portionsthereof being shown in section;

Fig. 6 is a vertical sectional view taken on the line 6--6 of Fig. 5;and

Fig. 7 is a plan view, partly in section, taken on the line 'l'! of Fig.5. V v M I This application is a continuation-impart of my copendingapplications Serial No. 639,475, filed January 5, 1946, and Serial No.98,528, filed June 11, 1949, both now abandoned.

Referring to Fig. l, the fume hood comprises a slab I forming theworking surface upon which the chemical apparatus producing toxic ofnoxious fumes is placed. The slab IE] is supported at a convenientheight from the floor by any suitable structure [2, which is usually inthe form or a cabinet or a chest of drawers, for instrumentsand-apparatus. The fume hood proper consists of a rear wall l4, a top[6, a front wall ['8 extending across the top portion only of the hood,and a glazed sash 20 which is slid'able in a suitable frame 22 andprovided with counterbalance weights in the usual manner of a windowsash. The hood includes a left side wall 24 and a right side wall 26.The slab, walls, top, and Window frame are secured together in thecustomary manner of cabinet construction.

The depth of the hood near its upper end is reduced by a vertical-Wall28 joined to a diagonal frame 30 secured to the lower edge of the frontwall l8 by a horizontal board 32. The frame 3i) holds an elongated sheetof glass 34 providing a window for a fluorescent lamp 36 enclosed in asuitable housing 38. L

Exterior baffles 40 and 42 extend outwardly at an angle of approximately45 degrees with respect to the plane of the sash frame, and are suitablysecured to the; vertical edges of the latter. A similar bafile 44 issimilarly secured at the front edge of the slab Ii]. These bailles forma funnel-like structure for the working opening beneath the sash 20.

Referring to Fig. 1, air and fumes are exhausted from the fume hood by asuction fan 45 driven by an electric motor 48, while atmospheric air issupplied to the fume hood by means of a fan or blower 50 driven by amotor 52, the suction fan being connected to the fume hood by a suitablepipe or conduit 54 which is provided with means, shown as a damper 51(Fig. 2), to regulate the flow. The fan or blower 50 i connected to thefume hood by a suitable duct or conduit 55 having a similar flowregulating cal ducts 53 and'5 9 built into the rear corners of theinterior of the hood by means of boards 50, 6|, 62. and 63, it beingnoted that the boards "BI and 62 are of greater width at the top andtaper in widthtoward the bottom, as is appar-' ent from the shape of theboard 62 shown in Fig. 4. The ducts '8 and 59 are thus of. progressivelydecreasing cross sectional area. The lower ends of the board 52 are cutaway to form ports 54 and 65 (Fig. 2) leading to a manifold or plenumchamber 55 formed between the slab H], the lower end of the back Wall[4, and a vertical board 63. The top of the plenum chamber is formed bya pair of similarly perforated boards 10 which are supported in spacedrelation by the board 68 and the rear wall I4, and which encloses asuitable air filtering material 72, such as spun glass.

Directly above, and extending the full length of the perforated boards76, is a diagonal lower baffle 14 suitably secured to the rear wall 14.An inclined intermediate baffle 15 is suitably secured to the boards GIand 62 approximately in alignment With the lower bafile 74, being spacedfrom the latter to provide an elongated horizontal secondary exhaustport iii. If desired, the effective width of the port l8 may be changedby an adjusting bafile 88.

An exhaust bafile 82 is in substantial alignment with the baffie i5 andspaced therefrom to provide a horizontal elongated exhaust port 84, andis spaced from the top Hi to provide a primary horizontal elongatedexhaust port 85. The baffle 82 is provided with a. plurality of slots 88which may be arranged as best shown in Fig. 2.

In using the fume hood, the motors, 48 and52 are energized to drive thefans 46 and 55, the controls for these motors preferably being soarranged that the suction blower or fan must be in operation before thepressure fan or blower is started. The capacities of these fans aresuch, and the dampers 55 and 5'! are so adjusted, that the blower fanforces into the hood approximately eighty per cent of the air which isWithdrawn from the hood by the exhaust or suction fan during a givenperiod. The air flowing through the conduit 55 is divided between thetwo ducts 58 and 59, and flow downwardly through these ducts atincreasing velocity into the plenum chamber 56 due to the tapering-crosssectional area of the ducts 58 and '59. In the plenum chamber 66, thevelocity pressure of the air is partially converted into staticpressureand this air flows through the perforations 'Hformed in thefilter board 10 in jets (at A) so that the static pressure is againconverted into velocity pressure, the jets expanding gradually in crosssectional area and flowing forwardly and upwardly into the fume hood asindicated by the arrows in the vicinity of B in Fig. 4. Due to the highvelocity of the jets emerging from the perforations H, a negativepressure is produced, as indicated by the arrows in the vicinity of C,the negative pressure at this place causing continuous flow of air alongthe top surface of the slab [0 to sweep this surface of any fumes whichmay be given off by chemicals placed in containers on the surface, orwhich may have been spilled on this surface. The smooth regular flow ofthis stream of air over the top surface of the slab I5. is improved bythe provision of the exterior baffle 44 which has a funneling effect andreduces, or substantially eliminates, turbulence along the frontedge ofthe slab IE3.

As the jets of air increase in cross sectional area, and consequentlylose some velocity, they are drawn upwardly as indicated by the arrowsin the vicinity of D, due to the negative pressure present in the spaceE behind the baifle 82. Air flowing through the working opening beneaththe sash 2&3 meets the air supplied through the perforationsin board illto produce a buffer zone F, indicatedby the light cross hatchedlines, in

which the pressure is but slightly negative with respect to the pressurein the room, so that the flow of air from the room through the openingbeneath sash 2G is of such low velocity that only approximately twentyper cent of the air and fumes exhausted through the conduit 54 is takenfrom the room in which the hood is located. In the region to the left(Fig. 4) of the zone F, there is substantial turbulence, as indicated bythe semi-circular arrows, so that the air forced into the fume hood, aswell as the air drawn through the working opening, intermix thoroughlywith the fumes, with resultant adequate dilution of the fumes, the fumesbeing indicated by the heavy arrows emanating from the crucible 92.

The baflie 82, although having openings of substantial aggregate crosssectional area, never theless affords a sufficient restriction to freeflow of air, that the flow of air is substantially uniform throughoutthe width of the hood even though the exhaust conduit 54 is connected tothe exhaust plenum chamber E at the center thereof.

The Venturi effect of the high velocity air jets from the openings 14 isof substantial advantage in that it assures continuous uniform flow ofair along the surface of slab ID.

The velocity of flow of air and fumes within and from the hood issufficiently great that the fumes, even though heavier than air, will beswept upwardly within the hood and exhausted from the exhaust chamber Ethrough the exhaust conduit as. This is true despite the fact that thevelocity of flow of air through the access opening is relatively low.Escape of fumes from the hood is precluded by virtue of the presence ofthe buffer or barrier zone indicated by the cross hatching and theletters F, and by virtue of the provision of the exterior baiiles 42,43, and 44, which,

through a funnel-like action, direct air toward the access opening andprevent turbulence immediately adjacent the access opening.

The invention may be embodied in variant forms, one such modificationbeing shown in Figs. 5, 6, and '7, wherein parts corresponding to thosepreviously described have had corresponding reference characters appliedthereto so that a repetition of the description of them will beunnecessary.

In the construction shown in these figures, the sash is provided by asingle sheet 94 of plate glass provided with handles 96 and is suitablycounterbalanced. The interior of the hood is rectangular in vertical aswell as horizontal cros section, and is provided with a solid baille S8and an apertured baffle lilll. These baffies are preferably mounted forpivotal movement between the positions in which they are shown in fulllines and the positions in which they are shown in dotted lines.

In this embodiment, the air under pressure is supplied through twovertical ducts I02 and I03, which at their lower ends communicate with aplenum chamber Hi4. Suitable elbow baffles I55 (Fig. 5) are preferablyprovided to induce laminar flow of the air and to cause it to flow atsubstantially uniform velocity as it enters the plenum chamber l 84.

Depending vertical baffles I68 of progressively increasing length fromthe sides toward the center are provided to induce substantially uniformdistribution of the air flow lengthwise of the plenum chamber I64. Airis discharged from the plenum chamber H64 through a nozzle H0 whichextends substantially the fullwidth of the fume hood between the ductsI02 and I03. Air emerging from the nozzle I I0 impinges in part againstthe lower edge of the baffle 98 so that at least some of the air flowsupwardly along the front surface of the bafiles 98 to provide someturbulence, indicated by the semi-circular shaped arrows. The majorportion of the jet from the nozzle I I0 flows in the space between therear wall of the housing and the bafiles 98 and H into anenlargedexhaust plenum chamber H2, and from thence to the exhaustconduit 54. The baffles 98 and [Di] are pivotally mounted so that bothsides thereof may bewashed by a water spray discharged from a nozzle I14.

The modified form of the invention shown in Figs. 5, 6, and 7, may beused where the gases are exhausted from the hood in part by convectionso that the capacity of the exhaust fan may be reduced, and in suchcases where the noise resultant from the discharge of air through thelarge number of jet orifices H of the first described embodiment wouldbe undesirable. Thus the fume hood shown in Figs. 5, 6, and 7, hasadvantages in particular installations, even though it will withdrawsubstantially more than twenty per cent (even as much as fifty per cent)of the exhausted air from the laboratory room. In such installations,where work at the table is intermittent so that the access opening maybe closed or substantially closed a large portion of the time, the formof the invention shown in Figs, 5, 6, and l, is very practical andefficient. However, the form of the invention shown in Figs. 1 to 4 willbe preferred Whenever all, or most, of the energy for exhausting thehood must be supplied mechanically, and especially in such installationsin which the sash is in its upper position most of the time, or in whichthe hood is not equipped with a sash to close the access opening.

In both embodiments of the invention, the amount of conditioned airremoved from the laboratory room is greatly reduced as compared withfume hoods of the prior art, the fumes generated in the hood are welldiluted, the air flows over the Working surface of the table atrelatively low velocity so as not to interfere with burner flames orunduly to cool heated apparatus placed on the work table, and escape offumes from the hood to the laboratory room is precluded.

While I have shown and described preferred embodiments of my invention,it will be apparent that numerous variations and modifications thereofmay be made without departing from the underlying principles of theinvention. I therefore desire, by the following claims, to includewithin the scope of the invention all such variations and modificationsby which substantially the results of my invention may be obtainedthrough the use of substantially the same or equivalent means.

I claim:

1. A fume exhaust hood comprising means forming a work surface, ahousing over said means having means to provide a front access openingto the work surface, blower means forcing air taken from the outsideatmosphere into said housing along the lower portion of the rear wallthereof, means along the lower rear wall of the housing to cause theatmospheric air entering the housing to form high velocity upwardlydirected jets, inclined bafile means extending along the rear of thehousing positioned to deflect the jets forwardly, the space between therear wall and said baffle means forming an exhaust plenum chamber, saidbafile means having a large number of exhaust openings of relativelylarge aggregate cross sectional area in the upper portion thereof topermit flow of air and fumes from the main portion of the housing to theplenum chamber, and suction means to create a negative pressure in theplenum chamber and connected to exhaust air and fumes therefrom to theoutside atmosphere, the capacity of said suction producing means beingsubstantially greater than that of the blower means so as to cause airto flow from the room in which the fume hood is located through theaccessopening into the housing at a relatively low velocity.

2. A fume exhaust hood comprising means forming a work surface, ahousing over said means having means to provide a front access openingto the work surface, blower means for forcing air taken from the outsideatmosphere into said housing along the lower rear wall thereof, meansalong the lower rear wall of the housing to cause the atmospheric airentering the housing to form high velocity upwardly directed jets,inclined baflie means extending along the rear of the housing positionedto deflect the jets forwardly, the space between the rear wall and saidbaffle means formin a plenum chamber, said baffle means having a largenumber of exhaust openings of relatively large aggregate cross sectionalarea in the upper portion thereof and a horizontal slot of smaller crosssectional area near the bottom thereof to permit flow of air and fumesfrom the main portion of the housing to the plenum chamber, and suctionmeans to create a negative pressure in the plenum chamber and to exhaustair and fumes therein to the outside atmosphere, the capacity of saidsuction producing means being approximately twenty-five per cent greaterthan-that of the blower means so as to cause approximately twenty percent of the gases exhausted to flow from theroomin which the fume hoodis located through the access opening into the housing.

3. In a-fume hood for use in a laboratory, the combination of meansforming a working surface for the reception-of apparatus and chemicalswhich may produce toxic or noxious fumes, means forming a housingoversaid surface and including a sash movable to position-to provide arelatively largeopen-ing at the-front'through which the laboratorytechnician may -haveaccess to' apparatus placed on the working surface,meansforming a plurality of apertures spaced along the rear wall nearthe loweredge thereof to produce upwardly directed jets of air,forwardly inclined bafile means extending across the housing in aposition to direct the air jets upwardly and forwardly, said bafflemeans having a plu-, rality of discharge openings in the upper portionthereof and together with the rear wall of the housing forming anexhaust plenumchamber, blower means for forcing air under pressure tothe jet'aper-ture forming-"means, and suction producing meansconnectedtosaid plenum chamberand to the outside atmosphere to exhaust air andfumesfrom the plenum chamber, theblower means, and the suction producingmeans being of such relative capacities that a negative pressure withrespect to that ofthe laboratory in which the hood is located isproduced within the front portion of the hood and such that approxi-vmately eighty per cent of the gases which are ex-v hausted from thehood; by the suction ,produc-- ing means will be atmospheric .air.supplied by the blower means, the remaining exhausted gases includingair withdrawn from the laboratory through the access opening and thefumes generated within the housing.

l. In a pressurized fume hood for a slab forming a work surface, thecombination of a housing having an opening for access to apparatusplaced on the work surface, means for supplying air under pressure in anupwardly directed stream near the rear edge of the slab, baffle means todeflect a portion of said stream of air forwardly, said baffle meansbeing apertured and forming with the housing an exhaust chamber, andmeans connected to the exhaust chamber to create a negative pressuretherein, the capacity of the last named means being slightly greaterthan that of the means for supplying air under pressure whereby a minorportion of the gases withdrawn from the exhaust chamber will be airdrawn thr ugh the access opening.

5. In a pressurized fume'hood for a slab forming a work surface, thecombination of a housing having an opening for access to apparatusplaced on the work surface, means for supplying air under pressure in anupwardly directed stream near the rear edge of the slab, bafile means todefiect a portion of said stream of air forwardly, said baffle meansbeing apertured and forming with the housing an exhaust chamber, meansconnected to the exhaust chamber to create a negative pressure therein,the capacity of the last named means being slightly greater than that ofthe means for supplying air under pressure whereby a minor portion ofthe gases withdrawn from the exhaust chamber will be air drawn throughthe access opening, and external baliies secured to the housing alongthe sides and bottom of the access opening shaped to funnel air into theaccess opening and to prevent excessive turbulence at the bottom andsides of the access opening.

6. A fume hood for a generally rectangular laboratory table comprising,a housing secured to the table and providing at its front an accessopening for manipulation of apparatus on the table, means for supplyingair under pressure to the housing in an upwardly directed stream alongthe lower rear edge of the table, baflie means to deflect a portion ofsaid air stream forwardly toward the central portion of the space withinthe housing, the upper portion of the baffle means having dischargeopenings therein and being spaced from the upper portion of the rearwall of the housing to provide an exhaust chamber, and means towithdrawgases from the exhaust chamber, the capacity of the last namedmeans being greater than that of the means for supplyin air underpressure, whereby air will flow into the hood through the accessopening.

'7. In a fume hood for a laboratory work table, the combination of meansforming a rear wall, two side walls, a top, and an adjustable front wallcapable of being moved to a position to provide an access opening to thespace above the work table, suction producing means, means forming anexhaust opening at the top and rear of the hood, means connecting theexhaust opening to the suction producing means to exhaust gases from thehood to the atmosphere, means forming air inlet openings near the rearof the work table to direct air upwardly, air pressure producing meansconnected to the inlet openings for causing flow of atmospheric airthereto, and apertured baliie meansextending from near the 9 lower endof the rear wall and inclined forwardly into close proximity to the top.

8. In a fume hood structure for laboratory work table slabs, thecombination of means forming a housing over the work surface of thetable, means forming a top, side walls, a rear wall, and an adjustableopening front wall in which the opening is directly above the work slabfor access to apparatus placed thereon, means communicating with theoutside atmosphere for producing positive and negative pressures,conduit means connecting the negative pressure producin means to thefume hood housing near the top and at the rear of the housing, conduitmeans connecting the positive pressure producing means to inlet openingsat the rear and at the bottom of the housing, an apertured inclinedbaffle means extending across the housing from the lower end of the rearwall substantially to the top of the housing in spaced relation to therear wall to provide a negative pressure plenum chamber in communicationwith the first conduit means, the apertures in the baffle means beinglocated mainly in the upper portion thereof and the lower edge of thebaiiie means being located above the inlet openings to cause some of theair discharged therefrom to pass upwardly behind the bailie means and tocause the remaining air discharged from the inlet openings to bedeflected forwardly to commingle with fumes which may be produced byapparatus placed on the work table, and means for adjusting the rate offlow of atmospheric air to the hood and the rate of exhaust of air fromthe hood to the atmosphere such that for a given period of time thevolume of gases exhausted from the hood will be twenty-five to onehundred per cent greater than the volume of air supplied by the positivepressure producing means, whereby some air will be drawn into the hoodthrough the access opening at the front thereof whenever the front wallis adjusted to provide such access opening.

HARRY S. MORROW.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,218,718 Throop Mar. 13, 19171,578,950 Bartling Mar. 30, 1926 1,741,954 Reymiller Dec. 31, 19291,847,736 Ward Mar. 1, 1932 1,934,808 Liptay Nov. 14, 1933 1,968,532Lipta-y July 31, 1934

